MEMS device having formations for covering actuators of the device

ABSTRACT

A micro-electromechanical device that comprises a substrate; an elongate actuator that has a fixed end that is connected to the substrate and a movable end, the actuator being configured so that the movable end is displaced relative to the substrate on receipt of an actuation signal; a motion-transmitting structure that is fast with the movable end of the actuator, the motion transmitting structure being connected to a working member so that movement of the actuator is translated to the working member; and a covering formation that is positioned on the substrate so that the substrate, the covering formation and the motion-transmitting structure define an air chamber, the actuator being positioned within the air chamber.

This is a Continuation application of U.S. Ser. No. 10/713,070 filed on Nov. 17, 2003.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

FIELD OF THE INVENTION

This invention relates to a micro-electromechanical device. More particularly, this invention relates to a micro-electromechanical device which incorporates covering formations for actuators of the device.

REFERENCED PATENT APPLICATIONS

The following patents/patent applications are incorporated by reference. 6,227,652 6,213,588 6,213,589 6,231,163 6,247,795 09/113,099 6,244,691 6,257,704 09/112,778 6,220,694 6,257,705 6,247,794 6,234,610 6,247,793 6,264,306 6,241,342 6,247,792 6,264,307 6,254,220 6,234,611 09/112,808 09/112,809 6,239,821 09/113,083 6,247,796 09/113,122 09/112,793 09/112,794 09/113,128 09/113,127 6,227,653 6,234,609 6,238,040 6,188,415 6,227,654 6,209,989 6,247,791 09/112,764 6,217,153 09/112,767 6,243,113 09/112,807 6,247,790 6,260,953 6,267,469 09/425,419 09/425,418 09/425,194 09/425,193 09/422,892 09/422,806 09/425,420 09/422,893 09/693,703 09/693,706 09/693,313 09/693,279 09/693,727 09/693,708 09/575,141 09/113,053 09/855,094 09/854,762 09/854,715 09/854,830 09/854,714 09/854,703 09/855,093 09/854,815 09/854,825 09/864,377 09/864,380 09/900,178 09/864,379 09/864,378 09/864,334 09/864,332 09/864,343 09/864,342 09/866,786 09/874,757 09/900,174 09/900,160 09/900,175 09/900,177 09/900,159 09/900,176 09/922,274 09/922,275 09/922,158 09/922,159 09/922,036 09/922,047 09/922,029 09/922,207 09/922,112 09/922,105 09/942,549 09/942,605 09/942,548 09/942,603 09/942,604

BACKGROUND OF THE INVENTION

As set out in the above referenced applications/patents, the Applicant has spent a substantial amount of time and effort in developing printheads that incorporate micro electro-mechanical system (MEMS)—based components to achieve the ejection of ink necessary for printing.

As a result of the Applicant's research and development, the Applicant has been able to develop printheads having one or more printhead chips that together incorporate up to 84 000 nozzle arrangements. The Applicant has also developed suitable processor technology that is capable of controlling operation of such printheads. In particular, the processor technology and the printheads are capable of cooperating to generate resolutions of 1600 dpi and higher in some cases. Examples of suitable processor technology are provided in the above referenced patent applications/patents.

The Applicant has overcome substantial difficulties in achieving the necessary ink flow and ink drop separation within the ink jet printheads. A number of printhead chips that the Applicant has developed incorporate nozzle arrangements that each have a nozzle chamber with an ink ejection member positioned in the nozzle chamber. The ink ejection member is then displaceable within the nozzle chamber to eject ink from the nozzle chamber.

A particular difficulty that the Applicant addresses in the present invention is to do with the delicate nature of the various components that comprise each nozzle arrangement of the printhead chip. In the above referenced matters, the various components are often exposed as a requirement of their function. On the MEMS scale, the various components are well suited for their particular tasks and the Applicant has found them to be suitably robust.

However, on a macroscopic scale, the various components can easily be damaged by such factors as handling and ingress of microscopic detritus. This microscopic detritus can take the form of paper dust.

It is therefore desirable that a means be provided whereby the components are protected. Applicant has found, however, that it is difficult to fabricate a suitable covering for the components while still achieving a transfer of force to an ink-ejecting component and efficient sealing of a nozzle chamber.

The Applicant has conceived this invention in order to address these difficulties.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a micro-electromechanical device that comprises

-   -   a substrate that incorporates drive circuitry;     -   an elongate actuator that has a fixed end that is connected to         the substrate so that the actuator can receive an electrical         signal from the drive circuitry and a movable end, the actuator         being configured so that the movable end is displaced relative         to the substrate on receipt of the electrical signal;     -   a motion-transmitting structure that is fast with the movable         end of the actuator, the motion transmitting structure being         connected to a working member so that movement of the actuator         is translated to the working member; and     -   a covering formation that is positioned on the substrate so that         the substrate, the covering formation and the motion         transmitting structure define an air chamber, the actuator being         positioned within the air chamber.

The covering formation may include walls that extend from the substrate and a cover that spans the walls. The motion-transmitting structure may be shaped so that the cover and the motion-transmitting structure define generally co-planar surfaces that are spaced from, and generally parallel to the substrate. An opening may be defined between the cover and the motion-transmitting surface to facilitate relative displacement of the cover and the motion-transmitting surface.

The actuator may include at least one elongate actuator arm of a conductive material that is capable of thermal expansion to perform work, the actuator arm having an active portion that defines a heating circuit that is connected to the drive circuitry layer to be resistively heated on receipt of the electrical signal from the drive circuitry layer and subsequently cooled on termination of the signal, and a passive portion which is insulated from the drive circuitry layer, the active and passive portions being positioned with respect to each other so that the arm experiences differential thermal expansion and contraction reciprocally to displace the movable member.

The motion-transmitting structure may define a lever mechanism and may have a fulcrum formation that is fast with the substrate and pivotal with respect to the substrate and a lever arm formation mounted on the fulcrum formation. An effort formation may be connected between the movable end of the actuator and the lever arm formation and a load formation may be connected between the lever arm formation and the working member.

The lever arm formation, the cover and the walls may define a unitary structure with the lever arm formation being connected to the walls with a pair of opposed torsion formations that are configured to twist as the lever formation is displaced.

The device may include nozzle chamber walls that are positioned on the substrate and a roof wall. The walls and the motion-transmitting structure may define a nozzle chamber and the roof wall may define an ejection port in fluid communication with the nozzle chamber. The working member may be in the form of a fluid ejection device that is positioned in the nozzle chamber, such that displacement of the working member results in ejection of fluid in the nozzle chamber from the ejection port. The substrate may define a fluid inlet channel in fluid communication with the nozzle chamber to supply the nozzle chamber with fluid.

The roof wall, the lever arm formation and the cover may be generally co-planar, with a slotted opening being defined between the roof wall and the lever arm formation to accommodate relative movement of the lever arm formation and the roof wall.

According to a second aspect of the invention, there is provided a printhead chip for an inkjet printhead, the printhead chip comprising

-   -   a substrate; and     -   a plurality of nozzle arrangements that is positioned on the         substrate, each nozzle arrangement comprising         -   nozzle chamber walls and a roof that define a nozzle chamber             with the roof defining an ink ejection port in fluid             communication with the nozzle chamber;         -   an ink-ejecting member that is positioned in the nozzle             chamber, the ink-ejecting member being displaceable towards             and away from the ink ejection port so that a resultant             fluctuation in ink pressure within the nozzle chamber             results in an ejection of ink from the ink ejection port;         -   at least one work-transmitting structure that is             displaceable with respect to the substrate and is connected             to the ink-ejecting member so that displacement of the work             transmitting structure results in displacement of the             ink-ejecting member;         -   an actuator that is connected to the work-transmitting             structure, the actuator being capable of displacing the work             transmitting structure upon receipt of an electrical drive             signal; and     -   air chamber walls and a covering formation that is positioned         over the actuator, the air chamber walls and the covering         formation defining an air chamber in which the actuator is         positioned, the roof, the work transmitting structure and the         covering formation together defining a protective structure         positioned in a common plane.

The invention is now described, by way of example, with reference to the accompanying drawings. The following description is not intended to limit the broad scope of the above summary.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 shows a sectioned, three dimensional view of a nozzle arrangement of a printhead chip, in accordance with the invention, for an inkjet printhead; and

FIG. 2 shows a three dimensional view of the nozzle arrangement of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

In the drawings, reference numeral 10 generally indicates a nozzle arrangement for a first embodiment of an ink jet printhead chip, in accordance with the invention.

The nozzle arrangement 10 is one of a plurality of such nozzle arrangements formed on a silicon wafer substrate 12 to define the printhead chip of the invention. As set out in the background of this specification, a single printhead can contain up to 84 000 such nozzle arrangements. For the purposes of clarity and ease of description, only one nozzle arrangement is described. It is to be appreciated that a person of ordinary skill in the field can readily obtain the printhead chip by simply replicating the nozzle arrangement 10 on the wafer substrate 12.

The printhead chip is the product of an integrated circuit fabrication technique. In particular, each nozzle arrangement 10 is the product of a MEMS—based fabrication technique. As is known, such a fabrication technique involves the deposition of functional layers and sacrificial layers of integrated circuit materials. The functional layers are etched to define various moving components and the sacrificial layers are etched away to release the components. As is known, such fabrication techniques generally involve the replication of a large number of similar components on a single wafer that is subsequently diced to separate the various components from each other. This reinforces the submission that a person of ordinary skill in the field can readily obtain the printhead chip of this invention by replicating the nozzle arrangement 10.

An electrical drive circuitry layer 14 is positioned on the silicon wafer substrate 12. The electrical drive circuitry layer 14 includes CMOS drive circuitry. The particular configuration of the CMOS drive circuitry is not important to this description and has therefore been shown schematically in the drawings. Suffice to say that it is connected to a suitable microprocessor and provides electrical current to the nozzle arrangement 10 upon receipt of an enabling signal from said suitable microprocessor. An example of a suitable microprocessor is described in the above referenced patents/patent applications. It follows that this level of detail will not be set out in this specification.

An ink passivation layer 16 is positioned on the drive circuitry layer 14. The ink passivation layer 16 can be of any suitable material, such as silicon nitride.

The nozzle arrangement 10 includes nozzle chamber walls 18 positioned on the ink passivation layer 16. A roof 20 is positioned on the nozzle chamber walls 18 so that the roof 20 and the nozzle chamber walls 18 define a nozzle chamber 22. The nozzle chamber walls 18 include a distal end wall 24, a proximal end wall 26 and a pair of opposed sidewalls 28. An ink ejection port 30 is defined in the roof 20 to be in fluid communication with the nozzle chamber 22. The roof 20 defines a nozzle rim 32 and a recess 34 positioned about the rim 32 to accommodate ink spread.

The walls 18 and the roof 20 are configured so that the nozzle chamber 22 is rectangular in plan.

A plurality of ink inlet channels 36, one of which is shown in the drawings, are defined through the substrate 12, the drive circuitry layer 14 and the ink passivation layer 16. The ink inlet channel 36 is in fluid communication with the nozzle chamber 18 so that ink can be supplied to the nozzle chamber 18.

The nozzle arrangement 10 includes a work-transmitting structure in the form of a lever mechanism 38. The lever mechanism 38 includes an effort formation 40, a fulcrum formation 42 and a load formation 44. The fulcrum formation 42 is interposed between the effort formation 40 and the load formation 44.

The fulcrum formation 42 is fast with the ink passivation layer 16. In particular, the fulcrum formation 42 is composite with a primary layer 46 and a secondary layer 48. The layers 46, 48 are configured so that the fulcrum formation 42 is resiliently deformable to permit pivotal movement of the fulcrum formation 42 with respect to the substrate 12. The layers 46, 48 can be of a number of materials that are used in integrated circuit fabrication. The Applicant has found that titanium aluminum nitride (TiAlN) is a suitable material for the layer 46 and that titanium is a suitable material for the layer 48.

The load formation 44 defines part of the proximal end wall 26. The load formation 44 is composite with a primary layer 50 and a secondary layer 52. As with the fulcrum formation 42, the layers 50, 52 can be of any of a number of materials that are used in integrated circuit fabrication. However, as set out above, the nozzle arrangement 10 is fabricated by using successive deposition and etching steps. It follows that it is convenient for the layers 50, 52 to be of the same material as the layers 46, 48. Thus, the layers 50, 52 can be of TiAlN and titanium, respectively.

The nozzle arrangement 10 includes an ink-ejecting member in the form of an elongate rectangular paddle 54. The paddle 54 is fixed to the load formation 44 and extends towards the distal end wall 24. Further, the paddle 54 is dimensioned to correspond generally with the nozzle chamber 22. It follows that displacement of the paddle 54 towards and away from the ink ejection port 30 with sufficient energy results in the ejection of an ink drop from the ink ejection port. The manner in which drop ejection is achieved is described in detail in the above referenced patents/applications and is therefore not discussed in any detail here.

To facilitate fabrication, the paddle 54 is of TiAlN. In particular, the paddle 54 is an extension of the layer 50 of the load formation 44 of the lever mechanism 38.

The paddle 54 has corrugations 56 to strengthen the paddle 54 against flexure during operation.

The effort formation 40 is also composite with a primary layer 58 and a secondary layer 60.

The layers 58, 60 can be of any of a number of materials that are used in integrated circuit fabrication. However, as set out above, the nozzle arrangement 10 is fabricated by using successive deposition and etching steps. It follows that it is convenient for the layers 58, 60 to be of the same material as the layers 46, 48. Thus, the layers 58, 60 can be of TiAlN and titanium, respectively.

The nozzle arrangement 10 includes an actuator in the form of a thermal bend actuator 62. The thermal bend actuator 62 is of a conductive material that is capable of being resistively heated. The conductive material has a coefficient of thermal expansion that is such that, when heated and subsequently cooled, the material is capable of expansion and contraction to an extent sufficient to perform work on a MEMS scale.

The thermal bend actuator 62 can be any of a number of thermal bend actuators described in the above patents/patent applications. In one example, the thermal bend actuator 62 includes an actuator arm 64 that has an active portion 82 and a passive portion. The active portion 82 has a pair of inner legs 66 and the passive portion is defined by a leg positioned on each side of the pair of inner legs 66. A bridge portion 68 interconnects the active legs 66 and the passive legs. Each leg 66 is fixed to one of a pair of anchor formations in the form of active anchors 70 that extend from the ink passivation layer 16. Each active anchor 70 is configured so that the legs 66 are electrically connected to the drive circuitry layer 14.

Each passive leg is fixed to one of a pair of anchor formations in the form of passive anchors 88 that are electrically isolated from the drive circuitry layer 14.

Thus, the legs 66 and the bridge portion 68 are configured so that when a current from the drive circuitry layer 14 is set up in the legs 66, the actuator arm 64 is subjected to differential heating. In particular, the actuator arm 64 is shaped so that the passive legs are interposed between at least a portion of the legs 66 and the substrate 12. It will be appreciated that this causes the actuator arm 64 to bend towards the substrate 12.

The bridge portion 68 therefore defines a working end of the actuator 62. In particular, the bridge portion 68 defines the primary layer 58 of the effort formation 40. Thus, the actuator 62 is of TiAlN. The Applicant has found this material to be well suited for the actuator 62.

The lever mechanism 38 includes a lever arm formation 72 positioned on, and fast with, the secondary layers 48, 52, 60 of the fulcrum formation 42, the load formation 44 and the effort formation 40, respectively. Thus, reciprocal movement of the actuator 62 towards and away from the substrate 12 is converted into reciprocal angular displacement of the paddle 54 via the lever mechanism 38 to eject ink drops from the ink ejection port 30.

Each active anchor 70 and passive anchor is also composite with a primary layer 74 and a secondary layer 76. The layers 74, 76 can be of any of a number of materials that are used in integrated circuit fabrication. However, in order to facilitate fabrication, the layer 74 is of TiAlN and the layer 76 is of titanium.

A cover formation 78 is positioned on the anchors 70, 88 to extend over and to cover the actuator 62. Air chamber walls 90 extend between the ink passivation layer 16 and the cover formation 78 so that the cover formation 78 and the air chamber walls 90 define an air chamber 80. Thus, the actuator 62 and the anchors are positioned in the air chamber 80.

The cover formation 78, the lever arm formation 72 and the roof 20 are in the form of a unitary protective structure 92 to inhibit damage to the nozzle arrangement 10.

The protective structure 92 can be one of a number of materials that are used in integrated circuit fabrication. The Applicant has found that silicon dioxide is particularly useful for this task.

It will be appreciated that it is necessary for the lever arm formation 72 to be displaced relative to the cover formation 78 and the roof 20. It follows that the cover formation 78 and the lever arm formation 72 are demarcated by a slotted opening 94 in fluid communication with the air chamber 80. The roof 20 and the lever arm formation 72 are demarcated by a slotted opening 96 in fluid communication with the nozzle chamber 22.

The lever arm formation 72 and the roof 20 together define ridges 98 that bound the slotted opening 96. Thus, when the nozzle chamber 22 is filled with ink, the ridges 98 define a fluidic seal during ink ejection. The ridges 98 serve to inhibit ink spreading by providing suitable adhesion surfaces for a meniscus formed by the ink.

The slotted openings 94, 96 demarcate a torsion formation 100 defined by the protective structure 92. The torsion formation 100 serves to support the lever mechanism 38 in position. Further, the torsion formation 100 is configured to experience twisting deformation in order to accommodate pivotal movement of the lever mechanism 38 during operation of the nozzle arrangement 10. The silicon dioxide of the protective structure 92 is resiliently flexible on a MEMS scale and is thus suitable for such repetitive distortion.

Applicant believes that this invention provides a printhead chip that is resistant to damage during handling. The primary reason for this is the provision of the protective structure 92, which covers the moving components of the nozzle arrangements of the printhead chip. The protective structure 92 is positioned in a common plane. It follows that when a plurality of the nozzle arrangements 10 are positioned together to define the printhead chip, the printhead chip presents a substantially uniform surface that is resistant to damage. 

1. A micro-electromechanical device that comprises a substrate; an elongate actuator that has a fixed end that is connected to the substrate and a movable end, the actuator being configured so that the movable end is displaced relative to the substrate on receipt of an actuation signal; a motion-transmitting structure that is fast with the movable end of the actuator, the motion transmitting structure being connected to a working member so that movement of the actuator is translated to the working member; and a covering formation that is positioned on the substrate so that the substrate, the covering formation and the motion-transmitting structure define an air chamber, the actuator being positioned within the air chamber.
 2. A device as claimed in claim 1, in which the covering formation includes walls that extend from the substrate and a cover that spans the walls, the motion-transmitting structure being shaped so that the cover and the motion-transmitting structure define generally co-planar surfaces that are spaced from, and generally parallel to the substrate, an opening being defined between the cover and the motion-transmitting surface to facilitate relative displacement of the cover and the motion-transmitting surface.
 3. A device as claimed in claim 2, in which the actuator includes at least one elongate actuator arm of a conductive material that is capable of thermal expansion to perform work, the actuator arm having an active portion that defines a heating circuit that is connected to the drive circuitry layer to be resistively heated on receipt of the actuation signal and subsequently cooled on termination of the signal, and a passive portion, the active and passive portions being positioned with respect to each other so that the arm experiences differential thermal expansion and contraction reciprocally to displace the movable member.
 4. A device as claimed in claim 3, in which the motion-transmitting structure defines a lever mechanism and has a fulcrum formation that is fast with the substrate and pivotal with respect to the substrate and a lever arm formation mounted on the fulcrum formation, an effort formation being connected between the movable end of the actuator and the lever arm formation and a load formation being connected between the lever arm formation and the working member.
 5. A device as claimed in claim 4, in which the lever arm formation, the cover and the walls define a unitary structure with the lever arm formation being connected to the walls with a pair of opposed torsion formations that are configured to twist as the lever formation is displaced.
 6. A device as claimed in claim 4, which includes nozzle chamber walls that are positioned on the substrate and a roof wall, the walls and the motion-transmitting structure defining a nozzle chamber and the roof wall defining an ejection port in fluid communication with the nozzle chamber, the working member being in the form of a fluid ejection device that is positioned in the nozzle chamber, such that displacement of the working member results in ejection of fluid in the nozzle chamber from the ejection port, the substrate defining a fluid inlet channel in fluid communication with the nozzle chamber to supply the nozzle chamber with fluid.
 7. A device as claimed in claim 6, in which the roof wall, the lever arm formation and the cover are generally co-planar, with a slotted opening being defined between the roof wall and the lever arm formation to accommodate relative movement of the lever arm formation and the roof wall. 